Re: [PATCH 2/2] futex: remove futex_cmpxchg detection

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Am 26.10.21 um 12:03 schrieb Arnd Bergmann:
From: Arnd Bergmann <arnd@xxxxxxxx>

Now that all architectures have a working futex implementation
in any configuration, remove the runtime detection code.

Signed-off-by: Arnd Bergmann <arnd@xxxxxxxx>

s390 part
Acked-by: Christian Borntraeger <borntraeger@xxxxxxxxxx>

---
  arch/arc/Kconfig              |  1 -
  arch/arm/Kconfig              |  1 -
  arch/arm64/Kconfig            |  1 -
  arch/csky/Kconfig             |  1 -
  arch/m68k/Kconfig             |  1 -
  arch/riscv/Kconfig            |  1 -
  arch/s390/Kconfig             |  1 -
  arch/sh/Kconfig               |  1 -
  arch/um/Kconfig               |  1 -
  arch/um/kernel/skas/uaccess.c |  1 -
  arch/xtensa/Kconfig           |  1 -
  init/Kconfig                  |  8 --------
  kernel/futex/core.c           | 35 -----------------------------------
  kernel/futex/futex.h          |  6 ------
  kernel/futex/syscalls.c       | 22 ----------------------
  15 files changed, 82 deletions(-)

diff --git a/arch/arc/Kconfig b/arch/arc/Kconfig
index 248389278e8f..f9413041686f 100644
--- a/arch/arc/Kconfig
+++ b/arch/arc/Kconfig
@@ -31,7 +31,6 @@ config ARC
  	select HAVE_ARCH_TRANSPARENT_HUGEPAGE if ARC_MMU_V4
  	select HAVE_DEBUG_STACKOVERFLOW
  	select HAVE_DEBUG_KMEMLEAK
-	select HAVE_FUTEX_CMPXCHG if FUTEX
  	select HAVE_IOREMAP_PROT
  	select HAVE_KERNEL_GZIP
  	select HAVE_KERNEL_LZMA
diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
index bb5d2c45477b..6448d311635d 100644
--- a/arch/arm/Kconfig
+++ b/arch/arm/Kconfig
@@ -93,7 +93,6 @@ config ARM
  	select HAVE_FTRACE_MCOUNT_RECORD if !XIP_KERNEL
  	select HAVE_FUNCTION_GRAPH_TRACER if !THUMB2_KERNEL && !CC_IS_CLANG
  	select HAVE_FUNCTION_TRACER if !XIP_KERNEL && !(THUMB2_KERNEL && CC_IS_CLANG)
-	select HAVE_FUTEX_CMPXCHG if FUTEX
  	select HAVE_GCC_PLUGINS
  	select HAVE_HW_BREAKPOINT if PERF_EVENTS && (CPU_V6 || CPU_V6K || CPU_V7)
  	select HAVE_IRQ_TIME_ACCOUNTING
diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
index 0efc501f77aa..6c3c2ff5cef8 100644
--- a/arch/arm64/Kconfig
+++ b/arch/arm64/Kconfig
@@ -193,7 +193,6 @@ config ARM64
  	select HAVE_PERF_USER_STACK_DUMP
  	select HAVE_REGS_AND_STACK_ACCESS_API
  	select HAVE_FUNCTION_ARG_ACCESS_API
-	select HAVE_FUTEX_CMPXCHG if FUTEX
  	select MMU_GATHER_RCU_TABLE_FREE
  	select HAVE_RSEQ
  	select HAVE_STACKPROTECTOR
diff --git a/arch/csky/Kconfig b/arch/csky/Kconfig
index 823d3d5a9e11..efd7c5feac8b 100644
--- a/arch/csky/Kconfig
+++ b/arch/csky/Kconfig
@@ -53,7 +53,6 @@ config CSKY
  	select HAVE_FUNCTION_TRACER
  	select HAVE_FUNCTION_GRAPH_TRACER
  	select HAVE_FUNCTION_ERROR_INJECTION
-	select HAVE_FUTEX_CMPXCHG if FUTEX && SMP
  	select HAVE_FTRACE_MCOUNT_RECORD
  	select HAVE_KERNEL_GZIP
  	select HAVE_KERNEL_LZO
diff --git a/arch/m68k/Kconfig b/arch/m68k/Kconfig
index 0b50da08a9c5..15a793c5b2dc 100644
--- a/arch/m68k/Kconfig
+++ b/arch/m68k/Kconfig
@@ -20,7 +20,6 @@ config M68K
  	select HAVE_ASM_MODVERSIONS
  	select HAVE_DEBUG_BUGVERBOSE
  	select HAVE_EFFICIENT_UNALIGNED_ACCESS if !CPU_HAS_NO_UNALIGNED
-	select HAVE_FUTEX_CMPXCHG if MMU && FUTEX
  	select HAVE_MOD_ARCH_SPECIFIC
  	select HAVE_UID16
  	select MMU_GATHER_NO_RANGE if MMU
diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
index 77a088d0a7e9..037fea9fac14 100644
--- a/arch/riscv/Kconfig
+++ b/arch/riscv/Kconfig
@@ -84,7 +84,6 @@ config RISCV
  	select HAVE_DMA_CONTIGUOUS if MMU
  	select HAVE_EBPF_JIT if MMU
  	select HAVE_FUNCTION_ERROR_INJECTION
-	select HAVE_FUTEX_CMPXCHG if FUTEX
  	select HAVE_GCC_PLUGINS
  	select HAVE_GENERIC_VDSO if MMU && 64BIT
  	select HAVE_IRQ_TIME_ACCOUNTING
diff --git a/arch/s390/Kconfig b/arch/s390/Kconfig
index f615c3f65f5a..1c9ecf619e04 100644
--- a/arch/s390/Kconfig
+++ b/arch/s390/Kconfig
@@ -164,7 +164,6 @@ config S390
  	select HAVE_FUNCTION_ERROR_INJECTION
  	select HAVE_FUNCTION_GRAPH_TRACER
  	select HAVE_FUNCTION_TRACER
-	select HAVE_FUTEX_CMPXCHG if FUTEX
  	select HAVE_GCC_PLUGINS
  	select HAVE_GENERIC_VDSO
  	select HAVE_IOREMAP_PROT if PCI
diff --git a/arch/sh/Kconfig b/arch/sh/Kconfig
index 6904f4bdbf00..93195d3368c0 100644
--- a/arch/sh/Kconfig
+++ b/arch/sh/Kconfig
@@ -34,7 +34,6 @@ config SUPERH
  	select HAVE_FAST_GUP if MMU
  	select HAVE_FUNCTION_GRAPH_TRACER
  	select HAVE_FUNCTION_TRACER
-	select HAVE_FUTEX_CMPXCHG if FUTEX
  	select HAVE_FTRACE_MCOUNT_RECORD
  	select HAVE_HW_BREAKPOINT
  	select HAVE_IOREMAP_PROT if MMU && !X2TLB
diff --git a/arch/um/Kconfig b/arch/um/Kconfig
index c18b45f75d41..c906250d4970 100644
--- a/arch/um/Kconfig
+++ b/arch/um/Kconfig
@@ -14,7 +14,6 @@ config UML
  	select HAVE_ARCH_SECCOMP_FILTER
  	select HAVE_ASM_MODVERSIONS
  	select HAVE_UID16
-	select HAVE_FUTEX_CMPXCHG if FUTEX
  	select HAVE_DEBUG_KMEMLEAK
  	select HAVE_DEBUG_BUGVERBOSE
  	select NO_DMA if !UML_DMA_EMULATION
diff --git a/arch/um/kernel/skas/uaccess.c b/arch/um/kernel/skas/uaccess.c
index a509be911026..9e37a7c05990 100644
--- a/arch/um/kernel/skas/uaccess.c
+++ b/arch/um/kernel/skas/uaccess.c
@@ -348,7 +348,6 @@ EXPORT_SYMBOL(arch_futex_atomic_op_inuser);
   * 0 - On success
   * -EFAULT - User access resulted in a page fault
   * -EAGAIN - Atomic operation was unable to complete due to contention
- * -ENOSYS - Function not implemented (only if !HAVE_FUTEX_CMPXCHG)
   */
int futex_atomic_cmpxchg_inatomic(u32 *uval, u32 __user *uaddr,
diff --git a/arch/xtensa/Kconfig b/arch/xtensa/Kconfig
index 0e56bad058fa..8ac599aa6d99 100644
--- a/arch/xtensa/Kconfig
+++ b/arch/xtensa/Kconfig
@@ -31,7 +31,6 @@ config XTENSA
  	select HAVE_DMA_CONTIGUOUS
  	select HAVE_EXIT_THREAD
  	select HAVE_FUNCTION_TRACER
-	select HAVE_FUTEX_CMPXCHG if !MMU && FUTEX
  	select HAVE_HW_BREAKPOINT if PERF_EVENTS
  	select HAVE_IRQ_TIME_ACCOUNTING
  	select HAVE_PCI
diff --git a/init/Kconfig b/init/Kconfig
index c0f55ea5a71f..538688598f2f 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -1597,14 +1597,6 @@ config FUTEX_PI
  	depends on FUTEX && RT_MUTEXES
  	default y
-config HAVE_FUTEX_CMPXCHG
-	bool
-	depends on FUTEX
-	help
-	  Architectures should select this if futex_atomic_cmpxchg_inatomic()
-	  is implemented and always working. This removes a couple of runtime
-	  checks.
-
  config EPOLL
  	bool "Enable eventpoll support" if EXPERT
  	default y
diff --git a/kernel/futex/core.c b/kernel/futex/core.c
index 25d8a88b32e5..926c2bb752bc 100644
--- a/kernel/futex/core.c
+++ b/kernel/futex/core.c
@@ -41,11 +41,6 @@
  #include "futex.h"
  #include "../locking/rtmutex_common.h"
-#ifndef CONFIG_HAVE_FUTEX_CMPXCHG
-int  __read_mostly futex_cmpxchg_enabled;
-#endif
-
-
  /*
   * The base of the bucket array and its size are always used together
   * (after initialization only in futex_hash()), so ensure that they
@@ -776,9 +771,6 @@ static void exit_robust_list(struct task_struct *curr)
  	unsigned long futex_offset;
  	int rc;
- if (!futex_cmpxchg_enabled)
-		return;
-
  	/*
  	 * Fetch the list head (which was registered earlier, via
  	 * sys_set_robust_list()):
@@ -874,9 +866,6 @@ static void compat_exit_robust_list(struct task_struct *curr)
  	compat_long_t futex_offset;
  	int rc;
- if (!futex_cmpxchg_enabled)
-		return;
-
  	/*
  	 * Fetch the list head (which was registered earlier, via
  	 * sys_set_robust_list()):
@@ -950,8 +939,6 @@ static void exit_pi_state_list(struct task_struct *curr)
  	struct futex_hash_bucket *hb;
  	union futex_key key = FUTEX_KEY_INIT;
- if (!futex_cmpxchg_enabled)
-		return;
  	/*
  	 * We are a ZOMBIE and nobody can enqueue itself on
  	 * pi_state_list anymore, but we have to be careful
@@ -1125,26 +1112,6 @@ void futex_exit_release(struct task_struct *tsk)
  	futex_cleanup_end(tsk, FUTEX_STATE_DEAD);
  }
-static void __init futex_detect_cmpxchg(void)
-{
-#ifndef CONFIG_HAVE_FUTEX_CMPXCHG
-	u32 curval;
-
-	/*
-	 * This will fail and we want it. Some arch implementations do
-	 * runtime detection of the futex_atomic_cmpxchg_inatomic()
-	 * functionality. We want to know that before we call in any
-	 * of the complex code paths. Also we want to prevent
-	 * registration of robust lists in that case. NULL is
-	 * guaranteed to fault and we get -EFAULT on functional
-	 * implementation, the non-functional ones will return
-	 * -ENOSYS.
-	 */
-	if (futex_cmpxchg_value_locked(&curval, NULL, 0, 0) == -EFAULT)
-		futex_cmpxchg_enabled = 1;
-#endif
-}
-
  static int __init futex_init(void)
  {
  	unsigned int futex_shift;
@@ -1163,8 +1130,6 @@ static int __init futex_init(void)
  					       futex_hashsize, futex_hashsize);
  	futex_hashsize = 1UL << futex_shift;
- futex_detect_cmpxchg();
-
  	for (i = 0; i < futex_hashsize; i++) {
  		atomic_set(&futex_queues[i].waiters, 0);
  		plist_head_init(&futex_queues[i].chain);
diff --git a/kernel/futex/futex.h b/kernel/futex/futex.h
index 040ae4277cb0..c264cbeab71c 100644
--- a/kernel/futex/futex.h
+++ b/kernel/futex/futex.h
@@ -27,12 +27,6 @@
  #define FLAGS_CLOCKRT		0x02
  #define FLAGS_HAS_TIMEOUT	0x04
-#ifdef CONFIG_HAVE_FUTEX_CMPXCHG
-#define futex_cmpxchg_enabled 1
-#else
-extern int  __read_mostly futex_cmpxchg_enabled;
-#endif
-
  #ifdef CONFIG_FAIL_FUTEX
  extern bool should_fail_futex(bool fshared);
  #else
diff --git a/kernel/futex/syscalls.c b/kernel/futex/syscalls.c
index 6f91a07a6a83..086a22d1adb7 100644
--- a/kernel/futex/syscalls.c
+++ b/kernel/futex/syscalls.c
@@ -29,8 +29,6 @@
  SYSCALL_DEFINE2(set_robust_list, struct robust_list_head __user *, head,
  		size_t, len)
  {
-	if (!futex_cmpxchg_enabled)
-		return -ENOSYS;
  	/*
  	 * The kernel knows only one size for now:
  	 */
@@ -56,9 +54,6 @@ SYSCALL_DEFINE3(get_robust_list, int, pid,
  	unsigned long ret;
  	struct task_struct *p;
- if (!futex_cmpxchg_enabled)
-		return -ENOSYS;
-
  	rcu_read_lock();
ret = -ESRCH;
@@ -103,17 +98,6 @@ long do_futex(u32 __user *uaddr, int op, u32 val, ktime_t *timeout,
  			return -ENOSYS;
  	}
- switch (cmd) {
-	case FUTEX_LOCK_PI:
-	case FUTEX_LOCK_PI2:
-	case FUTEX_UNLOCK_PI:
-	case FUTEX_TRYLOCK_PI:
-	case FUTEX_WAIT_REQUEUE_PI:
-	case FUTEX_CMP_REQUEUE_PI:
-		if (!futex_cmpxchg_enabled)
-			return -ENOSYS;
-	}
-
  	switch (cmd) {
  	case FUTEX_WAIT:
  		val3 = FUTEX_BITSET_MATCH_ANY;
@@ -323,9 +307,6 @@ COMPAT_SYSCALL_DEFINE2(set_robust_list,
  		struct compat_robust_list_head __user *, head,
  		compat_size_t, len)
  {
-	if (!futex_cmpxchg_enabled)
-		return -ENOSYS;
-
  	if (unlikely(len != sizeof(*head)))
  		return -EINVAL;
@@ -342,9 +323,6 @@ COMPAT_SYSCALL_DEFINE3(get_robust_list, int, pid,
  	unsigned long ret;
  	struct task_struct *p;
- if (!futex_cmpxchg_enabled)
-		return -ENOSYS;
-
  	rcu_read_lock();
ret = -ESRCH;




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